[Core] Fix property access on read-only Dictionary

[AThousandShips]

Read-only dictionaries can be modified with property access, like so:

var my_dict := { "a": 0 }
my_dict.make_read_only()
my_dict.a = 1

This seems to be an oversight (and can't find any reports on it), but this makes it aligned with how it works for const

[AThousandShips]

This would just silently fail before as it uses the read-only temporary

[dalexeev]

I'm not familiar with VariantInternal, but shouldn't the [] operator check for readonly? I think that the check should work not only in GDScript (variant_setget.cpp), but also in the core.

godot/core/variant/dictionary.cpp

Lines 82 to 83 in fe01776

	Variant &Dictionary::operator[](const Variant &p_key) {
	if (unlikely(_p->read_only)) {

[AThousandShips]

As explained above, it uses the temporary, it doesn't throw any errors for the operator version and there isn't a distinct set method (which there is for Array, and that handles the check), we can't really have an error here as we return a reference (nor is it reliable as such, as we could be accessing it by reading only, the operator[] can't check for assignment without some proxy)

It works in core as well, with the valid return, just like for any other checks like that, when using set on a Variant, but unfortunately it can't be enforced in any other way

[AThousandShips]

What we might want to do is add a check to get_or_add as it does mutate like that, will see about that separately

Edit: Writing up an improvement, adding a set method to Dictionary for safe usage in c++, and adding a check to get_or_add, will push soon

• [Core] Array and Dictionary set improvements #89653

[akien-mga]

Thanks!

[AThousandShips]

Thank you!